This patent application claims priority from Japanese Application No. 338994/2002, filed Nov. 22, 2002.
1. Field of the Invention
The present invention relates to a small-sized electromagnetic relay to be mounted on a substrate.
2. Background Art
One of the known types of electromagnetic relays for mounting on a substrate comprises a coil constituting an electromagnet, an iron core, a yoke, a movable iron member (armature) attracted by the electromagnet, a movable contact spring to return the movable iron member to its initial position, a movable contact coupled to the movable iron member, a stationary contact disposed opposite to the movable contact, a stationary contact terminal conductively coupled to the stationary contact to lead to the outside, and a movable contact terminal conductively coupled to the movable contact to lead to the outside, as disclosed in JP-UM-A-3-86545. The movable contact opens/shuts relative to the stationary contact by means of the attractive force of the electromagnet and the resilient action of the movable contact spring, so as to change the conductive state between the movable contact terminal and the stationary contact terminal.
This type of conventional electromagnetic relay typically has a construction as follows for the movable contact terminal and its surrounding area.
In a first arrangement as shown in the FIG. 8 of JP-UM-A-3-86545 for example, a plate-shaped movable contact spring is attached to the backside of the yoke, one end of the spring being provided with to a movable contact, and the other end of the spring extending externally beyond a flange of a coil bobbin (a member on which the coil is wrapped, also known as a spool). This other end of the movable contact spring provides a leading end of the movable contact terminal inserted into a through-bore of a substrate. In a second arrangement as shown in the FIG. 1 of JP-UM-A-59-103346 for example, a part of the yoke extends externally beyond the flange to provide a leading end.
In a third arrangement as shown in the FIG. 2(B) of JP-A-63-252333, the movable contact spring is attached to the backside of the yoke, furthermore, another member (a movable contact leading terminal) is attached to the backside of the movable contact spring. One end of this member extends externally beyond the flange to provide a leading end.
In these types of electromagnetic relay, the component of the terminal (the movable contact spring in the above first example, or another member in the above third example) is attached to the yoke by countersunk rivet as shown in the FIGS. 5A and 5B. As shown in the FIG. 5A, a protrusion 2 is formed by pressing (forging) on the member 1 of the yoke or the like, then the protrusion 2 is inserted into a through-bore 4 formed in the terminal component 3. Next, as shown in the FIG. 5B, a conical-tool is urged on the center of the top surface of the protrusion 2 to provide plastic deformation for forming a groove having a V-shaped cross-section, then the protrusion 2 is spread in its diameter direction. The outer surface of the protrusion 2 is attached tightly to the inner surface of the through-bore 2 to fix the terminal component 3 to the member 1. This countersunk rivet feature is advantageous in that it is effective even when the height of the protrusion 2 is not sufficient relative to the thickness of the terminal component 3, and in that this feature is relatively easy to manufacture. However, it cannot urge the terminal component 3 on the member, 1, thus, the terminal component 3 cannot be tightly attached to the member 1.
The convention electromagnetic relay mentioned above suffers a number of disadvantages. First, the heat generated mainly in the coil or in the movable contact spring cannot be efficiently dissipated to the outside (the substrate side, for example) through the movable contact terminal, that is, the relay cannot dissipate the heat efficiently. Particularly, if a relay is designed for high current, the relay must have a large size as a whole to suppress the rise in its temperature. The large-sized relay needs a large substrate for mounting it, and the large substrate, in turn, needs a large housing for accommodation.
In the above-mentioned first arrangement, the movable contact spring serves as a movable contact terminal as well, which generates much heat that cannot be efficiently dissipated. The movable contact spring must be thin and made from a material suitable for a spring (material with low heat-conductivity such as copper alloy having low copper contents) in order to ensure flexibility.
Therefore when high current flows through the spring, it generates significant heat and the heat thus generated cannot readily escape to the outside.
In the above-mentioned second arrangement, the yoke serves as a movable contact terminal as well, which also dissipates hardly the generated heat. The yoke must be made from a material suitable for a magnetic body in order to attain a feature as an electromagnet (material such as pure iron having low heat-conductivity), so that the generated heat cannot readily escape to the outside.
In the above-mentioned third arrangement, the movable contact terminal consists of another member attached to the backside of the movable contact spring which, in turn, is attached to the yoke. Again, this arrangement cannot dissipate the generated heat efficiently. The heat from the yoke is transferred to another member via a member having low heat-conductivity (i.e. the movable contact spring), then be transferred through this another member to the outside. The heat must pass through the movable contact spring on the way to the outside, which prevents the heat from dissipating efficiently.
Also the conventional countersunk rivet feature as shown in the FIGS. 5A and 5B, has only limited contact area, that is, the areas which couple these two members are only the outer surface of the protrusion 2 and the inner surface of the through-bore 4 are closely attached. These two members attached via the countersunk rivet feature themselves do not attach tightly to each other. Thus, the members attached have low heat-conductivity, which also makes it difficult for the generated heat to be dissipated to the outside in the conventional electromagnetic relay therefore having limitation.
An electromagnetic relay of the invention comprising a coil constituting an electromagnet, an iron core, a yoke, a movable iron member (armature) attracted by an electromagnet, a movable contact spring to return the movable iron member to its initial position, a movable contact coupled to the movable iron member, a stationary contact disposed opposite to the movable contact, a stationary contact terminal conductively coupled to the stationary contact to lead to the outside, and a movable contact terminal conductively coupled to the movable contact to lead to outside, wherein the movable contact opens/shuts relative to the stationary contact by means of the attractive force of the electromagnet and the resilient action of the movable contact spring, so as to change the conductive state between the movable contact terminal and the stationary contact terminal, characterized in that;
a plate section which is coupled to at least one side of the yoke is formed in the movable contact terminal, the movable contact terminal being coupled to the yoke at one or more particular point(s) of the plate section by countersunk rivet feature(s);
the movable contact spring is coupled to the surface on the plate section opposite to the yoke; and
the countersunk rivet feature is formed by inserting a protrusion formed on the yoke into a countersunk hole formed on the plate section, and crushing the top of the protrusion to increase the diameter so as to sandwich the plate section against the yoke.
According to the electromagnetic relay of the present invention, the movable contact terminal contacts tightly to the yoke with wider contact area with intensified strength than in the conventional electromagnetic relay, which provides significantly enhanced heat-conductivity between the yoke and the movable contact terminal. Furthermore, the hole of the movable contact terminal constituting the countersunk rivet feature has a countersunk form, so that the movable contact terminal can have sufficient thickness without compromising function of above-mentioned countersunk rivet feature even when the protrusion of the yoke cannot have sufficient height due to limit in the pressing. This arrangement can maintain high productivity while remarkably enlarging the cross-section of the movable contact terminal to the lead end. The movable contact terminal is a separate member from the movable contact spring and the yoke, so that it is possible to make it with a material having high heat-conductivity such as pure copper, which provides extremely high heat-conductivity from the movable contact terminal to the substrate or the like.
Also, according to the electromagnetic relay of the invention, the movable contact spring is directly coupled to the movable contact terminal. This arrangement provides high heat-conductivity between the movable contact spring and the movable contact terminal.
Thus, the heat generated at the coil is transferred to the yoke through the iron core, then, to the substrate or the like via the movable contact terminal for efficient dissipation. The coil and the yoke are free from accumulation of the heat. Also, the heat generated in the movable contact spring by the current flowing therethrough is transferred to the substrate or the like and radiated with grate efficiency via the movable contact terminal which is directly coupled thereto in a same manner without accumulated in the moveable contact spring.
Therefore, a small-sized, high productivity electromagnetic relay affording high-current with little rise in its temperature can be achieved by the invention.
Preferably, the positions where the movable contact terminal is coupled to the yoke via the countersunk rivet feature are three or more than three which are not aligned on a line on the plate section. This arrangement improves tightness in the contact between the movable contact terminal and the yoke.